Structural-Biochemical Characterization of the Alolactic Enzyme of Streptococcus Mutans

Abstract

Most lactic acid bacteria (LAB) catalyze the decarboxylation of L-malate to L-lactate through a malolactic enzyme (MLE) that is dependent on NAD+ and Mn2+. This enzyme plays a crucial role in malolactic fermentation (MLF), a secondary fermentation process that occurs when L-malate and acidity are present. MLF enables the bacteria to prevent cytosolic acidification and establish a pH gradient across the cell membrane, driving ATP synthesis. This process is essential in the industrial production of wines, ciders, cheeses, and yogurts, enhancing the nutritional and organoleptic properties of the final products. Additionally, MLF impacts human health as part of the physiology of Streptococcus mutans, the bacterium responsible for dental caries, where MLF is considered a virulence factor. Currently, MLF is a spontaneous and difficult-to-control phenomenon, primarily due to the lack of information on the biochemical properties of MLE. Identifying the conditions and/or molecular components that modulate MLE activity could transform this fermentation into a controlled process. In this study, we present an optimized protocol to obtain MLE from S. mutans (SmMLE) without co-purification with other similar proteins, such as endogenous malic enzyme, which could interfere with its characterization.